FontDialog.FontMustExist Property

Private Sub Button1_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles Button1.Click

    ' Set FontMustExist to true, which causes message box error 
    ' if the user enters a font that does not exist. 
    FontDialog1.FontMustExist = True 

    ' Set a minimum and maximum size to be 
    ' shown in the FontDialog.
    FontDialog1.MaxSize = 32
    FontDialog1.MinSize = 18

    ' Show the Apply button in the dialog.
    FontDialog1.ShowApply = True 

    ' Do not show effects such as Underline 
    ' and Bold.
    FontDialog1.ShowEffects = False 

    ' Save the existing font. 
    Dim oldFont As System.Drawing.Font = Me.Font

    ' Show the dialog and save the result. 
    Dim result As DialogResult = FontDialog1.ShowDialog()

    ' If The OK button in the Font dialog box is clicked,  
    ' set all the controls' fonts to the chosen font by 
    ' calling the FontDialog1_Apply method. 
    If result = DialogResult.OK Then
        FontDialog1_Apply(Me.Button1, New System.EventArgs)

        ' If the Cancel button is clicked, set the controls' 
        ' fonts back to the original font. 
    ElseIf (result = DialogResult.Cancel) Then 
        Dim containedControl As Control
        For Each containedControl In Me.Controls
            containedControl.Font = oldFont
        Next 

    End If 
End Sub 

' Handle the Apply event by setting all controls' fonts to  
' the chosen font.  
Private Sub FontDialog1_Apply(ByVal sender As Object, _
    ByVal e As System.EventArgs) Handles FontDialog1.Apply

    Me.Font = FontDialog1.Font
    Dim containedControl As Control
    For Each containedControl In Me.Controls
        containedControl.Font = FontDialog1.Font
    Next 
End Sub

FontDialog.MaxSize, FontDialog.ShowEffects and FontDialog.FontMustExist members and handling the Apply event. To run this example paste the following code in a form